Several factors to consider the plants are currently dialled in and enjoying light nutrient ppm and temps or they wouldn't be lush green. Lowering light intensity would require a complete system adjustment from ppm light distance cycle duration. @McLovin777 if they are happy plants which they appear to be why suggest a change in light intensity?
First off for those curious the plants are used to it and a 1000w MH is spectrum perfect run at full wattage so reducing watts means new bulbs if you want correct spectrum
Secondly the plants are eating and drinking at a certain speed based on light intensity and temps, so lowering intensity means they eat and drink less.
Third the flood table isn't letting medium get too wet or too dry adjusting lights means cooler temps so medium has potential to get and stay too moist creating issues where there are none.
Here's what I want you to consider going from 1000 to 400 is suggesting changing an environmental influence by 60% and with HID bulbs it is changing lumens from 110,000-130,000 to less than 35,000
Your plants would almost halt growth until they readjusted to light and temps would exhibit multiple stress signs which would start leading you down the rabbit hole into wonder land hunting for Alice
If it isn't broke don't fix it this is why we post support tickets to hunt for flaws and broken things that are out of place